On the Influence of X-Ray Galaxy Clusters in the Fluctuations of the Cosmic Microwave Background

The negative evolution found in X--ray clusters of galaxies limits the amount of available hot gas for the inverse Compton scattering of the Cosmic Microwave Background (the Sunyaev--Zel'dovich effect). Using a parametrisation of the X-ray luminosity function and its evolution in terms of a coalescence model (as presented in the analysis of a flux limited X-ray cluster sample by Edge et al. 1990), as well as a simple virialised structure for the clusters (which requires a gas to total mass fraction \approxgt 0.1 in order to reproduce observed properties of nearby clusters) we show that the Compton distortion $y$ parameter is about two orders of magnitude below the current FIRAS upper limits. Concerning the anisotropies imprinted on arcmin scales they are dominated by the hottest undetected objects. We show that they are negligible ({\Delta T\over T}\approxlt 10^{-7}) at wavelengths \lambda\approxgt 1~mm. At shorter wavelengths they become more important (${\Delta T\over T}\sim 10^{-6}$ at $\lambda\sim 0.3$~mm), but in fact most clusters will produce an isolated and detectable feature in sky maps. After removal of these signals, the fluctuations imprinted by the remaining clusters on the residual radiation are still much smaller. The conclusion is that X-ray clusters can be ignored as sources of Cosmic Microwave Background fluctuations.Comment: 20 pages Plain Tex, 7 figures available upon request,UCAST-94-0

Soft versus Hard X-ray emission in AGN: partial covering and warm plus cold absorber models

We analyse the ROSAT PSPC hardness ratio and the 0.5-2 keV to 2-10 keV flux ratio of 65 Active Galactic Nuclei (AGN) for which there are both ROSAT archival observations available and 2-10 keV fluxes, mostly from the HEAO-1 MC-LASS survey. We conclude that the simplest spectral model for the AGN that can accommodate the variety of X-ray colours obtained is a standard power law (with energy spectral index $\alpha\sim 0.9$) plus a $\sim 0.1$ keV black body both partially absorbed. In our sample, type 1 AGN require an absorbing column around $10^{22}\, {\rm cm}^{-2}$ with covering fractions between 20 and 100\%, while type 2 AGN display larger columns and $\sim 100\%$ coverage. This simple model also provides a good link between soft and hard AGN X-ray luminosity functions and source counts. We also consider a warm absorber as an alternative model to partial covering and find that the the presence of gas in two phases (ionized and neutral) is required.Comment: 10 pages, Latex (mn.sty), 1 table, 5 figures included (epsf), postscript version also available via anonymous ftp at ftp://astsun1.unican.es/pub/ceballos/ . Accepted for publication in MNRA

X-ray sources as tracers of the large-scale structure in the Universe

We review the current status of studies of large-scale structure in the X-ray Universe. After motivating the use X-rays for cosmological purposes, we discuss the various approaches used on different angular scales including X-ray background multipoles, cross-correlations of the X-ray background with galaxy catalogues, clustering of X-ray selected sources and small-scale fluctuations and anisotropies in the X-ray background. We discuss the implications of the above studies for the bias parameter of X-ray sources, which is likely to be moderate for X-ray selected AGN and the X-ray background (~1-2). We finally outline how all-sky X-ray maps at hard X-rays and medium surveys with large sky coverage could provide important tests for the cosmological models.Comment: Invited review presented at the Workshop X-ray Astronomy'99: Stellar endpoints, AGN and the diffuse X-ray background (Astrophys Lett and Comm

Influence of wettability on liquid water transport in gas diffusion layer of proton exchange membrane fuel cells (PEMFC)

Water management is a key factor that limits PEFC's performance. We show how insights into this problem can be gained from pore-scale simulations of water invasion in a model fibrous medium. We explore the influence of contact angle on the water invasion pattern and water saturation at breakthrough and show that a dramatic change in the invasion pattern, from fractal to compact, occurs as the system changes from hydrophobic to hydrophilic. Then, we explore the case of a system of mixed wettability, i.e. containing both hydrophilic and hydrophobic pores. The saturation at breakthrough is studied as a function of the fraction of hydrophilic pores. The results are discussed in relation with the water management problem, the optimal design of a GDL and the fuel cell performance degradation mechanisms. We outline how the study could be extended to 3D systems, notably from binarised images of GDLs obtained by X ray microtomography

Methods And Systems For Enhancing Feed-conversion-ratio In Animals Using Mobile Enzyme Sequestration Platforms (MSEP)

A method for enhancing the enzymatic efficiency of an enzyme added to poultry feed for a living subject, comprises adding a cellulose-degrading enzyme to a mobile enzyme sequestration platform (MESP) so as to form an enzyme-MESP complex; adding the enzyme-MESP complex to poultry feed for a living subject; the enzyme efficiency of the cellulose-degrading enzyme of the enzyme-MESP complex after being exposed to a first adverse environment for a first period of time is at least 50% higher than the enzyme efficacy of the cellulose-degrading enzyme independent of the MESP being exposed to the first adverse environment for the first period of time

Methods And Systems For Enhancing Feed-conversion-ratio In Animals Using Mobile Enzyme Sequestration Platforms (MSEP)

A method for enhancing the enzymatic efficiency of an enzyme added to poultry feed for a living subject, comprises adding a cellulose-degrading enzyme to a mobile enzyme sequestration platform (MESP) so as to form an enzyme-MESP complex; adding the enzyme-MESP complex to poultry feed for a living subject; the enzyme efficiency of the cellulose-degrading enzyme of the enzyme-MESP complex after being exposed to a first adverse environment for a first period of time is at least 50% higher than the enzyme efficacy of the cellulose-degrading enzyme independent of the MESP being exposed to the first adverse environment for the first period of time